(1) Field of the Invention
This invention is directed to the field of optics and more particularly, to a low-strain, armored, fiber optic cable.
(2) Description of the Prior Art
In the heretofore known armored fiber optic cables, two locations in the cable core have been used to provide protection for the fibers. One location is at the center of the cable core, where fibers may be helixed around a king wire in the center of the core or laid longitudinally in a metal tube which forms the center of the cable core. The second location is outside the center of but still within the cable core, where the fiber is helixed around the core and either protected in an interstice between electrical connectors or contained in a helixed metal tube near the center of the cable core. When such an armored cable is stressed, the cable core undergoes a larger strain than the armor. To reduce strain on optical fibers located in the cable core, they are commonly stranded at a high angle with respect to the cable axis, but the higher the helix angle, the smaller the radius the fiber experiences in the cable core. For small radii, bend-induced optical attenuation may result. Another adverse effect of the heretofore known armored optical fiber cables arises when the cable is first worked, in that a residual construction strain appears in the cable core due to cable elongation when the armor wires set themselves into the cable core jacket. This residual strain undesirably remains in the cable core after initial use.